Electronic meter systems have been developed, as for example the systems disclosed in U.S. Pat. No. 3,978,457 for MICROCOMPUTERIZED ELECTRONIC POSTAGE METER SYSTEM, in U.S. Pat. No. 3,938,095 for COMPUTER RESPONSIVE POSTAGE METER, in U.S. Pat. No. 4,301,507 for ELECTRONIC POSTAGE METER HAVING PLURAL COMPUTING SYSTEMS and in European patent application, Publication No. 0 019 515 for ELECTRONIC POSTAGE METER HAVING IMPROVED SECURITY AND FAULT TOLERANCE FEATURES.
Each of the electronic postage meters disclosed in the above-identified application and patents include a nonvolatile memory for retaining stored critical information when power is not applied to the meter. Various types of accounting information may be stored in the meter's nonvolatile memory. This information includes, for example, the amount of postage remaining in the meter for subsequent printing and the total amount of postage printed by the meter. Other types of accounting or operating data may also be stored in the nonvolatile memory. The function served by the nonvolatile memory circuits have replaced and enhanced the functions of the mechanical accounting registers or wheels utilized in previous mechanical type postage meters.
It has been recognized that during the assembly of electronic postage meters that it may be desirable to enter the serial number into the nonvolatile memory of the meter upon completion of the assembly operation. It is found that this can be done in electronic postage meters. In one such arrangement, a nonvolatile memory chip number is entered into the nonvolatile memory and is used during the assembly of the meter. The meter itself, however, is assembled with the final serial number on the meter body still utilizing a nonvolatile memory with a given chip number entered in the serial number field. When assembly and testing is completed, the final serial number is communicated to the meter.
It is also noted that a flag bit can be set if the path to the serial number in the nonvolatile memory is to be closed off so that the data field in the nonvolatile memory occupied by the serial number cannot be written. That is, writing into nonvolatile memory in the data field containing the serial number is prevented. Such a system is disclosed in U.S. patent application, Ser. No. 238,331 filed Feb. 26, 1981, now U.S. Pat. No. 4,424,,573, issued Jan. 3, 1984, for Alton B. Eckert, Jr. and Edward C. Duwel, and entitled "SYSTEM FOR ENTERING A POSTAGE METER SERIAL NUMBER INTO A NONVOLATILE MEMORY FROM AN EXTERNAL CHANNEL AFTER ASSEMBLY OF THE METER".
It has also been recognized that it may be desirable to provide methods and apparatus which enable the changing of a serial number in a meter until it is finally determined that the entered serial number is correct. This allows flexibility in case of erroneous key stroke and avoids loss in having meters fail the final assembly point because of inadvertent error which would require the entire meter to be disassembled to access the nonvolatile memory in the meter. Such methods and apparatus are disclosed in U.S. Pat. No. 4,506,329 to Duwel et al for NONVOLATILE MEMORY SERIAL NUMBER LOCK FOR ELECTRONIC POSTAGE METER.
According to the teachings of the '329 patent a serial number may be entered into the meter at the end of the manufacturing process after the meter has been assembled and the components tested by actuation of a routine programmed into a read only memory within the meter. This routine is used only once during the life of the meter nonvolatile memory. The routine requires the check of a nonvolatile memory bit position which is set once the routine has been successfully completed. The setting of this bit prevents reentry into the one time program. The program can be reused until the bit is set. The bit is set by comparison of the data included in a received message with the value of data contained in memory. If the comparison is true, the bit is set. The format of the received message entered into the meter to enter the serial number and set the bit requires an external message generator. The particular message format employed cannot be generated by actuation of the meter keyboard.
Furthermore, in accordance with the invention disclosed in the '329 patent, the serial number message format includes one digit as an operational indicator. If the serial number has been entered and the operational indicator is set to zero, the serial number in the random access memory of the meter will be changed to the value contained in the data message. If the operational indicator is set to a one, the firmware will cause the meter to operate to examine the serial number presently contained in the random access memory image of the nonvolatile memory and compare it with the value contained in the serial number message. If the result is favorable or true, the program will set the nonvolatile memory lock bit image in the random access memory thus preventing further access into this program once the image is written into the meter's nonvolatile memory.